如何处理不可能引发的检查异常

Question

I want to new a url object, and do something with the url.

For example,

void downloadPage()
{
    URL url=new URL("http://www.google.com");
    do(url);
}

The code doesn't compile because the URL constructor declares MalformatedException , I have to either declare the exception or try-catch it. But I think none of two ways make sense, because the url string doesn't change, this exception is impossible to be thrown.

How should I deal with this situation?

Answer 1

You can do this:

try {
    throwsCheckedException();
} catch(CheckedException e) {
    throw new RuntimeException(e);
}

This way the exception is still thrown if you are wrong but you don't have to deal with it if you are really sure it won't happen. This is probably not appropriate for production code. If the program is important to someone that's not you, a better solution may be to log it in the appropriate manner.

You really can't be sure an exception will never throw, I've personally had it happen a couple of times where I was pretty sure it wouldn't and it did.

The other way is to handle it in a sissy way:

// in some utility class
public static void exitWithError(Throwable e, String msg) {
    dumpStackTraceToFile(e); // something you should have
    JOptionPane.showMessageDialog(null, msg);
    System.exit(1); // force JVM exit when the dialog closes
}

// wherever this should be, only do it once
static final URL GOOGLE;
static {
    try {
        GOOGLE = new URL("http://google.com");
    } catch(MalformedURLException e) {
        exitWithError(e, "Somebody changed the Google URL!");
    }
}

Answer 2

You could just surround it in a try/catch like so from my understanding.

void downloadPage()
{

try {

  URL url=new URL("http://www.google.com");
   do(url);

} catch(MalformedException me) { 
     System.out.println("caught this: " + me);
}


}

Answer 3

Try catching it is the best way to go about it. This also protects you in case you accidentally edit the url to http//www.google.com .

Answer 4

You have to declare it or try-catch it. There is no other way.

Compiler is not able to "check" if your address is malformated or not before running it.